Messages in this thread | | | Date | Mon, 24 Oct 2022 14:03:03 +0800 | Subject | Re: [PATCH v2 1/2] mm: migrate: Fix return value if all subpages of THPs are migrated successfully | From | Baolin Wang <> |
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On 10/24/2022 9:56 AM, Huang, Ying wrote: > Yang Shi <shy828301@gmail.com> writes: > >> On Fri, Oct 21, 2022 at 11:41 AM Andrew Morton >> <akpm@linux-foundation.org> wrote: >>> >>> On Fri, 21 Oct 2022 18:16:23 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote: >>> >>>> When THP migration, if THPs are split and all subpages are migrated successfully >>>> , the migrate_pages() will still return the number of THP that were not migrated. >>>> That will confuse the callers of migrate_pages(), for example, which will make >>>> the longterm pinning failed though all pages are migrated successfully. >>>> >>>> Thus we should return 0 to indicate all pages are migrated in this case. >>>> >>> >>> This had me puzzled for a while. I think this wording is clearer? >>> >>> : During THP migration, if THPs are not migrated but they are split and all >>> : subpages are migrated successfully, migrate_pages() will still return the >>> : number of THP pages that were not migrated. This will confuse the callers >>> : of migrate_pages(). For example, the longterm pinning will failed though >>> : all pages are migrated successfully. >>> : >>> : Thus we should return 0 to indicate that all pages are migrated in this >>> : case. >>> >>> This is a fairly longstanding problem? No Fixes: we can identify? >> >> It doesn't seem like a long standing issue. It seems like commit >> b5bade978e9b ("mm: migrate: fix the return value of migrate_pages()") >> fixed one problem, but introduced this new one IIUC. >> >> Before this commit, the code did: >> >> nr_failed += retry + thp_retry; >> rc = nr_failed; >> >> But retry and thp_retry were actually reset for each retry until the >> last one. So as long as there is no permanent migration failure and >> THP split failure, nr_failed should be 0 IIUC. TBH the code is a >> little bit hard to follow, please correct me if I'm wrong. > > I think that you are correct. We can added > > Fixes: b5bade978e9b ("mm: migrate: fix the return value of migrate_pages()")
I think so too. Thanks Yang and Ying for pointing it out.
> >>> Did you consider the desirability of a -stable backport? > > I think this can be backport to -stable.
Agree.
Andrew, could you help to add the Fixes tag and cc -stable? Thanks.
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